Which Tehillim is said on Rosh Chodesh?

Aneinu

Rosh Chodesh is the first day of any month in the Jewish Calendar (which follows the lunar cycle). Psalm 104 is a song of praise to G-d for the creation of the universe and its continued sustenance. One could say that the celebration of a new month reflects this aspect of G-d’s perpetual relationship with the world.

Tehillim: Kappitel קד